During a data transmission process in a network, after downloading a data packet from the network, an acknowledgment (ACK) for the downloaded data is commonly required from the receiving electronic device. When an obvious gap exists between an uplink bandwidth and a downlink bandwidth, the uplink bandwidth may be not wide enough to send the ACK. This may lead to the transmission of the ACK being delayed (as pending in the network) and only a certain number of the ACKs can be successfully sent. Downloading speed is thereby limited. For example, the full speed for downloading data based on the downlink bandwidth may be promoted as one hundred data packets per second, but the speed of uploading ACKs based on the uplink bandwidth can be only thirty ACKs per second. The actual downloading speed will be limited to be thirty data packets per second, and some data packets need to be held in a delay window.